Published literature on union catalogs indicates that applicable cost effectiveness studies of union catalogs is non-existent. Hence, this project proposes research on the specific trade - off between the costs of maintenance and the benefits of union catalog systems. The Midwest Medical Union Catalog will serve as the sample union catalog for this study. Interlibrary loan request samplings for monographic materials received by the Midwest Regional Medical Library Service will be arranged and studied in relation to the Midwest Medical Union Catalog from the viewpoint of various relevant hypotheses. The results of these studies will affirm or negate the proposed hypotheses, and will also supply specific data upon which to base decisions related to effectiveness or ineffectiveness of the union catalog as an appropriate location tool.